1. 4 | ISSUE N°144 | 25/04/2013
EQUIPMENT & MATERIALS
Thermo compression bonding technologies
Thermo-compression bonding (TCB) technology is a fascinating alternative to the established C4 ßip-chip technology with
mass reßow.
T
CB can master a couple of challenges which
would be show stoppers for C4:
• TCB is capable for ultra-Þne pitch Cu-
pillar ßip chip (40 pitch and less)
• Based on local reflow TCB can deal with
warped (thin) die and warped substrate,
which is normally a no-go for mass reßow
• 22 nm CMOS nodes and below are especially
sensitive to silicon/substrate CTE mismatch
stress, which can be signiÞcantly reduced
by the TCB gradient bonding method (which
is not an available option for mass reßow)
TCB bonding has been introduced in mass
production in combination with NCP (non-
conductive paste) pre-application. This is a
smart approach to overcome the voiding issues
of capillary underfill (CUF) for fine bump
pitches. The TCB process, however, gets very
challenging for ultra-thin dies like for TSV
memory stack production, as the bleed can
climb up to the top of the die. For this reason
there are lots of activities to replace NCP by
NCF (non-conductive foil). NCF, however,
demands for higher bond force, which - in
combination with 30 thin die - does not make
people feel very conÞdent. For this reason the
step back to post-applied underfill like CUF
(capillary underÞll) can be frequently observed,
but also MUF (molded underÞll) becomes more
and more attention. The Fico molding machine
of our sister company is already capable to
underÞll gaps of 30 thickness.
Challenges and opportunities
Thermo-compression comes with a lot of
technical challenges. In contrast to the
current C4 flip-chip technology thermo-
compression requires much higher forces,
while at the same time demanding a Þve-fold
increase in placement accuracy. Another
crucial requirement is high co-planarity of
bond head and pedestal, as well as a
sophisticated bond control which is capable of
smoothly switching between bond force
control and bond height control.
Besi/Datacon has chosen a unique approach
to tackle this challenge. In contrast to the
usual approach of building heavy and stiff
systems by adding sufficient mass to the
mechanical structures, Besi/Datacon uses a
patented mechatronic approach which is based
on light weight machine design, proper
kinematics and enhanced servo control. This
approach allows unique opportunities to end-
up with a high speed thermo-compression
bonder which has small footprint while
maintaining exceptional placement accuracy at
high bond forces. The mechatronic approach
is not only capable to tackle the high accuracy/
high bond force/productivity challenge. It also
allows for an automatic tilt diagnostic
procedure at any bond location, and automatic
adjustment of the bond head tilt.
Finally, the mechatronic approach of the
Datacon 8800 CHAMEO TC allows dual head
bonding on a single substrate, which is a
unique advantage for the processing of high
density substrate with pre-applied NCP, as it
avoids NCP dry-out because of the double
throughput of the substrates.
Ready for high volume production?
Our customers give us a clear message about
the requirements for high volume production:
TCB bonding needs to run robustly with high
yield, and it needs to become as easy and
productive as C4 ßip-chip bonding. High yield
is related to the TCB “core capabilities” which
are high accuracy, automated co-planarity,
bond control and thin die handling. All these
capabilities are in place, but in order to
maintain a robust production process
throughput is usually compromised, even if
the machine could run at a higher speed. TC
bonders must be equipped with sufficient
diagnostics for capability integrity in order to
utilize maximum machine productivity without
compromising the yield. As most TC products
are still in a pilot phase and not in mass
production, a Þnal statement about readiness
for high volume production will clearly have
some limits in confidence level. The big
challenge is to run steep mass production
ramps with the guarantee that the production
equipment does not vary from tool to tool.
This will be the next focus where vendors of
thermo-compression bonders have to
concentrate their attention.
www.besi.com
Fully automatic thermo-compression production line (Courtesy of Besi)
The equipment & materials business
Equipment & Materials for
3DIC & Wafer-Level-Packaging
Dr. Hugo
Pristauz,
Vice president
of Besi Flip Chip
division.
D r . P r i s t a u z
h e l d v a r i o u s
management positions in Besi R&D
and Marketing since 1999, among
others being responsible for the
complete development of the
highly successful 8800 platform.
Today as Vice President of the Flip
Chip division he is responsible for
the development and marketing
activities of all Besi flip chip
equipment. Dr. Pristauz holds a
PhD in electrical engineering with a
main focus on control engineering.
After graduation he worked as a
university teacher before starting
a career in the semiconductor
industry.